High purity carbon dioxide is an important chemical used extensively by the food and beverage industry, and, amongst other things, for PH control in wastewater treatment and as a carbon source in chemical manufacturing. Carbon dioxide is used to carbonate soft drinks and liquid carbon dioxide is expanded to freeze fresh foods. The primary sources of carbon dioxide are by-product streams from chemical processes, natural underground formations and combustion gases. Combustion gases are the oldest and most widely available source.
Heretofore, attempts to recover carbon dioxide from exhaust gases were by processes using a chemical solvent to scrub the gas and thereafter distilling to recover the carbon dioxide. Such methods are costly and meet with problems regarding corrosion and solvent degradation. Examples of such processes and methods to alleviate the corrosion problems are found in U.S. Pat. No. 2,065,112 which issued in 1936, U.S. Pat. No. 2,399,142 which issued in 1946, U.S. Pat. No. 2,377,966 which issued in 1945, U.S. Pat. No. 4.477.419 which issued in 1948, U.S. Pat. No. 3,137,654 which issued in 1964. The alkanolamine process described in some of these patents is still widely used today.
More recently, commercial membrane technology has been developed for separating acid gases like carbon dioxide and hydrogen sulfide from light hydrocarbon gases. Examples of such art are found in U.S. Pat. No. 4,130,403 which issued Dec. 19, 1978 to T. E. Cooley et.al., U.S. Pat. No, 4,639,257 which issued Jan. 27, 1987 to Melvyn Duckett et.al., and U.S. Pat. No. 5,233,837 which issued Aug. 10, 1993 to Richard Callahan. The features of these patents, particularly the use of membrane separation, was a definite step forward in the carbon dioxide separation art. However, the prior art in this field continues to suffer from overall efficiency of the process and undesirable membrane life. These problems have been significantly mitigated by the apparatus and process of this invention.